RECORDS. 377 



ments on Dcntaliinn leave by analogy little doubt that such a 

 causal connection exists. We do not in the least know how 

 these protoplasmic stuffs or materials act. We can hardly 

 imagine how it is that one kind of stuff involves the develop- 

 ment of muscles, others that of nerves, ciliated cells, or shell- 

 secreting cells. We may guess that these stuffs may be anal- 

 ogous to the so-called internal secretions, formed in the adult 

 organism by such organs as the thyroid or the sexual glands, 

 which are known to produce quite specific morphological effects 

 on the body. A second guess is that the formative stuffs may 

 be related to the soluble ferments or enzymes, which in other 

 ways play so great a role in the economy of plants and animals. 

 But, aside from this question, the evidence is steadily increas- 

 ing, I think, that such stuffs exist, that they have a definite ar- 

 rangement in the Qgg, and that in cases where the form of 

 cleavage is constant they are distributed in a definite way to the 

 cells into which the Qgg splits up. The cleavage-mosaic is 

 accordingly to be conceived as an actual mosaic of different 

 materials that are somehow causally connected with develop- 

 ment of particular parts. When these materials are equally 

 distributed by the earlier divisions, as in Amphioxus, each of 

 the resulting cells may upon isolation produce a perfect larva ; 

 when they are unequally distributed, as in Dcntaliuin, the cells 

 are no longer equivalent, and upon being isolated produce the 

 structures corresponding to the particular stuffs allotted to them.^ 

 These facts will presently bring us to our first general conclu- 

 sion. First, if the protoplasm contain such stuffs, grouped and 

 distributed in a definite way, to just this extent may develop- 

 ment receive a mechanical interpretation — that is, be conceived 

 as the result of an antecedent material configuration in the egg- 

 protoplasm. We have as yet no very distinct idea regarding 

 the degree of complexity of this initial protoplasmic configura- 

 tion, though there are facts that indicate that it may not be very 



1 It will appear in the sequel that even in the latter case the potentiality of pro- 

 ducing a complete embryo may still be present in the nucleus. It is important to 

 distinguish between such primary or original nuclear potentiality, which may be 

 common to all the cells, and the secondary or immediate potentiality determined by 

 protoplasmic specification. The relation between these is still an unsolved problem. 



